Students in introductory biomechanics courses are expected to learn conceptual and procedural knowledge about how people move and how people move better (i.e., more skillfully and more safely). The basic content knowledge comes from biology (e.g., anatomy), physics (e.g., mechanics), and the integration of the two (i.e., biomechanics). The application of this content to help people move better depends on the systematic use of procedures. Traditional curricula have not been adequate, however, for reaching the expected ends in our courses. This may be, in part, because the available materials are static rather than dynamic and the concomitant points of emphasis have not cohered into a tenable system for application. Therefore, funds were sought from the Center for Excellence in Learning and Teaching at CSU, Chico to develop dynamic, digital exemplars of movement; these were intended to be integral to a biomechanics curriculum that was designed for systematic application. Selected examples and discussion of the project are presented here:
A major goal of this section of our course is for students to learn a procedure for deducing what muscles are active during movement. Common weight lifting exercises are frequently used for examples and analysis because they are relatively uncomplicated and relevant to students on both personal and professional levels. The exercise shown here is a "lat pull down."
If the students work through the deductive procedure properly with this movement, they should conclude that the latissimus dorsi muscle is one of the prime movers for the lat pull down. (It is surprising how often students who are grinding through the process with this exemplar have a mini-epiphany about how this common exercise got its name.)
The first step in the procedure is to determine the plane of activity. To do this, the students first need to know the names and locations of the primary or cardinal planes (which are shown below with a model from the Poser program). In our weight lifting example, the action at the shoulder joint is in the frontal plane.
Once the plane is identified, the observed action in that plane is specified. The animated model below is demonstrating the two actions at the shoulder joint in the frontal plane: abduction and adduction. Thus the observed action in the lat pull down is adduction as the bar is pulled down and abduction as the bar is allowed to rise by virtue of the attached cable and pulley.
Determining the plane of activity is relatively straightforward when the activity begins or ends in the anatomical position (which is depicted in the diagram of the cardinal planes). In actuality, however, we perform many movements in which segments of the body do not approach the anatomical position. In these cases we must refer to secondary, segmental planes. The nature of segmental planes is demonstrated in the animation below: These planes are parallel to (or coincident with) the primary planes when in the anatomical position but remain embedded in each segment as it becomes reoriented in space. Thus while the thigh is in the anatomical position, its segmental planes are essentially parallel to the cardinal planes. However, once the thigh begins to abduct, the sagittal (green) and transverse (dark blue) segmental planes, which remain embedded, are no longer parallel to their cardinal planes. (Because the segmental frontal plane does not deviate from parallel with its cardinal plane during this motion, one can deduce that the motion is in the frontal plane.)
The concept of the locally embedded plane is especially important for movements of the shoulder joint. In the animation below, the arm has been abducted such that its dark blue transverse plane, which was horizontal in the anatomical position, has become vertical. Thus the actions which are seen here -- medial (inward) and lateral (outward) rotation -- are in the transverse plane. In some cases it is easier to imagine the axis rather than the plane of action. To highlight the relationship between a plane and its axis, the longitudinal axis is shown in red as it runs long-wise through the upper arm and perpendicular to the localized transverse plane.
Motions of the upper arm (i.e., the humerus) at the shoulder joint are typically accompanied by motions in the shoulder girdle (i.e., the scapula and clavicle). This is because the socket of this ball-and-socket joint is on the scapula, and it must reorient at times for the ball (on the humerus) to have full range of motion. For example, the humerus can abduct at the shoulder joint by about 60° without movement in the scapula, but after that, the scapula should upwardly rotate about 1° for every 2° of abduction. This relationship (known as scapulohumeral rhythm) is especially difficult to observe. Hence the Poser program was used to generate the animation of scapulohumeral rhythm below. When the muscles that cause upward rotation of the scapula become fatigued or otherwise inoperative (e.g., from swimming too many laps), normal scapulohumeral rhythm tends to break down and injuries (e.g., from shoulder impingement) are common.
The terms translation and rotation are introduced early in most biomechanics texts. However, the typical examples are outside the experience of most readers because pure translation and rotation are relatively rare. It may be more useful to use the "squinty-eyed" approach to see how regular people translate and rotate in the general -- but not pure -- sense. Bowling is an exemplar activity for both these motions. In the home movie below, one can see that the bowler's arm mostly rotates backward and forward as the bowler as a whole translates toward the pins.
As an aid to clarity of understanding, these concepts were accentuated with graphical overlays on the movie. In the movie below, the bowler's arm was overlaid with a yellow line in each frame so that rotation could be emphasized. Similarly the translatory path of the shoulder joint was traced with a red line as the bowler approached the pins. For the first portion of the approach, the red line is relatively flat; then, as the bowler nears release, the red line dips down somewhat.
Not only did the graphical overlays help students connect with mechanical concepts, but they also helped the mover improve his movement: Upon seeing the red line in this movie, the bowler realized that he had altered his approach due to his arthritis. That gave him an idea about how he could modify his approach to be more effective. After a bit of practice, he bowled a 300 game!
Frames from the bowling movie were extracted and overlaid with graphics to illustrate the relationship between angular and linear motion (see below). The position of the bowler's arm in three separate frames was again represented by a yellow line. The predominantly angular path of the ball before release was shown in magenta, and the curvilinear path of the ball after release was shown in green. According to physics, the initial linear path of the ball after release will be tangential to the arc before release or at right angles to the radius of rotation (i.e., the arm rotating at the shoulder joint) at release. The light blue arrows depict what the initial path of the ball would have been if the ball had been released at the precise instant that an image was captured; instead, the ball must have been released at an instant in between images to follow the green path of projection.
The timing of release is often important whether the projectile is a human or a ball. The first movie below, taken from the 2000 Olympics, shows the effect of holding on to the high bar for hundredths of seconds too long. The second movie, which has been circulating on the internet, shows the effect of holding on for tenths of seconds too long. If you play this movie frame by frame and use the angular-linear relationship illustrated by the bowling example, you can compare the positions when release should have occurred and when it did occur.
As moving humans we are subject to the laws of both biology and mechanics. And we can describe our movement using ten core concepts which lie at the intersection of biology and mechanics. Not only are these concepts measurable (qualitatively with the eye and quantitatively with instruments), but they matter if we wish to move more skillfully or safely. Thus knowledge of the core concepts is very useful in the systematic application of biomechanics.
Snapshots from our bowling movie can be used to illustrate range of motion, one of the most important concepts. In the first picture below, the frames when the forward swing of the arm began and finished were extracted and combined. These positions represent the extreme ranges of motion for the primary phase of bowling. Because the arm was also translating as it rotated, it is somewhat difficult to observe the angle through which the arm moved. Therefore, using technology magic, the background was removed and the separate pictures of the bowler were repositioned such that the shoulder joint was at the same place for both frames. That allows us to better see the angle (of approximately 240°) that the bowler's arm went through as he propelled the bowling ball.
Once one understands the concept of range of motion, it is time to try to see it in action. How would you describe the range of motion during the crouch of the jump in the movie below?
As you can see, making eyeball assessments of movement in real time is difficult. Thus it can be quite beneficial to practice observing movement using slow motion or stop action. (With QuickTime movies one can control the speed of play by regulating the rate of tapping on the right-arrow key.) Also, as a general rule, it is easier to observe the whole body (i.e., somatic focus) or a large area of the body (i.e., sectional focus) instead of a single part of the body (i.e., segmental focus). The different levels of focus are illustrated in the pictures below, which were taken from the movie of the jump above: Depth of descent is a somatic measurement because it is based on how far the center of the whole body moves. Knee flexion is a sectional measurement because it is based on movement in the legs -- a large section of the body. The angle of trunk inclination is based on movement in a single (though large) segment. Depending on the situation, any one of these indicators of range of motion might be appropriate for observation.
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With practice and opportunities to validate one's observations, range of motion can be assessed with relative ease and accuracy. On the other hand, coordination, which is another of the ten core concepts, is easy to notice in the extremes but difficult to discern accurately. As you watch the movie of Shaquille O'Neal below, you may notice that he does not seem to be as coordinated as he could be. That is the easy part. The hard part is observing why. If you use relatively slow motion and focus at the segmental level, you may notice some peculiarities of sequencing (e.g., using larger segments after, rather than before, smaller ones) and timing (e.g., stopping a segment and then starting it again).
According to Kuhn (1970), one of the most effective ways of teaching science is through the use of exemplars. That is, a principle can be well illustrated by a situation in which the points of emphasis are relatively obvious and few confusing factors are present. And, as we have seen, graphical overlays can strengthen the emphasis. Additionally, by using material that is available through simulation (e.g., the animated skeleton), or on the internet (e.g., the unfortunate high bar episode), or on television (e.g., the underwater view of Olympic swimmers below), or archived (e.g., the conversion from film of Suzanne Lenglen playing tennis in the 1920s below) one can illustrate situations that are virtually impossible to observe in one's daily life.
With dynamic exemplars one can also show a sense of continuity. For example, an event that happens early in an activity (such as a delayed release position on a high bar) can affect an event that happens later (such as an undesirable position on return to the high bar). Or characteristics of movement that happen at different times can be clustered together to form patterns. In the movie below, one sees a child who is throwing a bean bag. She is not using her legs at all (i.e., low number of segments), her feet are side-by-side (i.e., relatively stable balance), her trunk range of motion is restricted, and her motions are predominately simultaneous and in the sagittal plane. These characteristics all fit the pattern of a novice thrower. In addition, they fit the pattern of someone who is being very conservative. More than likely this child has chosen to keep her legs fairly immobile and her feet in place, which then restricts her trunk movement and limits rotations outside the sagittal plane, in order to preserve her balance -- which is a conservative, and initially wise, choice for someone with severely impaired sight.
Another benefit of using exemplars is that one can silently shape perception through them. In biomechanics it is common to idealize elite athletes. This is associated with beliefs that we should all try to be like Mike (Jordan, that is) and that deviations from the idealized form are flaws that need to be corrected (as though we were machines in need of repair). These attitudes are more difficult to sustain if the exemplars encompass the full diversity of movers and movements. Thus it is beneficial to see movers of different genders, ages, shapes, races, eras, and abilities/disabilities as they engage in all manner of movements from sport and exercise to work and daily living. Over time one begins to realize that most of us, including the fabulously talented, can improve our technique if we have reasons to do so, and that some people of limited abilities have developed excellent technique despite their limitations. Perhaps this realization comes sooner if one has access to exemplary performances such as Shaq shooting free throws (above) and the boy throwing a small football from the wheelchair below.
Although it is possible to compile dynamic exemplars using analog video sources, there is much to be said for having one's own digital video camera, computer, and software. Aside from quality issues, digital video affords better access, convenience, and manipulability. That is, digital video can be distributed over the internet or email to an unlimited number of people, and they can view it at any time on virtually any computer. Moreover, they can view it at a variety of speeds, and they can create and print snapshots if they desire. It is also easy to combine or superimpose pictures and add titling or other graphic embellishments with free or very low cost software.
In addition, having a digital camera enables one to convert old analog video to digital as well as to make original digital movies. When students are the stars of their own movies, the potential for learning accelerates. As an example, we took individual movies of the students in lab as they sprinted. Almost immediately we held a series of brief student-teacher conferences to point out things that they were doing well and things that they might be able to do better. In the same week each student received a QuickTime movie of the sprint and a composite picture such as the one below. By juxtaposing two consecutive positions of "toe-off" with an 8-foot ruler and frame numbers, the students were able to compute their stride length, stride rate, and average velocity.
From the moment that the sprinting pictures were distributed, there was an unmistakable surge in interest in biomechanics, and it did not abate. The student shown above decided -- with no prompting -- to make the stick figure animation of his sprint shown below. (The fact that he had never used any of the necessary software did not seem to be a deterrent.)
In one way or another, we were able to advantageously incorporate each of the seven principles of good practice in undergraduate education through the addition of digital video to our biomechanics class. As mentioned previously, the use of exemplars is a means of emphasizing time on task. In short, moving pictures are worth more than a thousand words. And starring in many mini-movies and a major movie (i.e., a term project to improve one's movement using systematic application of course content) is the epitome of active learning.
Although some of our lab experiences were intentionally self-centered, other experiences were collaborative. For example, students worked in small groups as they learned how to do muscular analysis. With each step in the procedure (i.e., planes/axes, joint actions, type of tension, etc.), they were able to analyze and discuss sample movies such as the one of the lat pull down above. As we shifted to a more mechanical perspective and faster movements, they experimented with a sliding-scale method to rate each of their cohorts on range of motion in jumping (see above). Then, after they had printed key snapshots and measured their actual range of motion, they shared this information with their cohorts so they could validate or adjust their strategies of observation. In this manner they were using digital video to obtain prompt feedback about their skill in observation.
Over the span of the semester we collected video of the students on many days as they did many things. Often there was interaction between the students and teacher about the movement. And even when there was not, the teacher learned more about the students and their movement during video processing and grading. This seemed to add a level of intimacy that was appreciated by the students. As a gesture toward reciprocity, a couple of old movies of the teacher-as-athlete were converted to digital format and added to the set of exemplars. The movie below is an example of manipulating balance to slow down and stop before crossing a line.
The decision to incorporate dynamic exemplars raised expectations in many ways. For instance, students could be expected to master more challenging material because they should need less time to learn basic concepts. With the increased attention to visual materials, the students could be expected to demonstrate better observational skills and greater success in analyzing movement. And with these improved conceptual and analytic abilities, the students might learn to synthesize and evaluate movers and their movements with near-professional competence. (Note: Most professionals seem to be deficient at this.)
But for the students to approach the level of professional competence, expectations would have to be raised for the teacher as well: The dynamic exemplars would need accompanying material, and all of this would need to be readily and incrementally available. Thus a WebCT site was developed to distribute the new materials as soon as they were generated. (This vehicle was particularly appropriate because exemplar movies and accompanying material could be posted to the site and used in and out of class and because individual movies and the like could emailed to each student.) Over the span of the semester the teacher learned to use WebCT and digital video, scanning, and image processing hardware and software and generated hundreds of student movies in addition to a web site with 23 exemplar movies, 67 original and 77 borrowed graphics, and 231 print pages. The students were not oblivious to this effort on their behalf, and they had little choice but to raise their self-expectations. We all seemed to appreciate our mutual learning society. (And most of us are glad to have future access to these materials.)
The majority of students in biomechanics classes have extensive experience moving and watching others move. Consequently, their kinesthetic and visual talents are apt to be relatively well developed. This should be advantageous inasmuch as the professional practice of biomechanics is very visual. Yet biomechanics is traditionally taught with verbal and quantitative methods. No wonder that we have a dismal record of educating agents of change in movement. The alternative tested here was to put visual variables at the center of the curriculum. Thus students could connect their embodied knowledge with class content, integrate the separate sciences of anatomy and mechanics around a common theme, and develop a systematic process for evaluating and prescribing movement based on what was known and what was observed. The results were very encouraging: The students' general knowledge of biomechanics, as indicated by verbal and quantitative exam scores, improved by 17% over the previous class which did not have dynamic exemplars. (More than likely, they would have done even better if the exams had had a visual component. ) The students' ability to apply biomechanical knowledge, as indicated by grades on term projects, improved by 15%. Interest and engagement were also demonstrably higher in the students who learned visually-based biomechanics. This method seems to form a natural bridge between the talents and experience that the students bring to the class and the skills and knowledge that they need upon exit. In addition, their happiness and sense of security as they cross the bridge seems to enable them to extend themselves to learn helpful but less natural things as they move along. How else can one explain the skateboard dude who expressed genuine gratitude for being assigned a set of physics word problems?
